The present invention is directed to bags for the containment of particulate or granular material, in particular to valve bags.
A valve bag is a flexible bag container having a body portion of substantially tubular configuration, which typically has an outer layer of at least one ply, and an inner layer of at least one ply. Typically, the plies may be made from a relatively stiff and sturdy, yet flexible, paper material, such as kraft paper. Valve bags are typically utilized for the transportation of bulk material that is granular, powdery, or particulate in form.
One end of the bag (usually the end the ultimate consumer opens) may be cut in a stepped end pattern, folded over and sealed to form what is called a pinch-bottom bag. Alternatively, the end may be formed with two sets of flaps, arranged in opposed pairs. The first pair of opposed flaps are folded inwardly toward one another (in-folded flaps). The two other flaps (outer flaps), typically oriented perpendicular to the in-folded flaps, would be folded over the already folded in-folded flaps and glued in place to close that end of the bag. Typically, in its flattened configuration, the end of the bag will assume a generally hexagonal shape, thus leading to such bags typically being called "diamond-bottom" bags. When such a bag is filled, the bottom of the bag will assume a square-bottom shape, although the length of the bag will not have specifically defined panels but may be generally tubular with an elongated oval cross-section.
Rather than leave the opposite end of the bag completely open for filling by the manufacturer/purchaser of the unfinished bag, the bag end can be filled with the opposite (purchaser) end of the bag substantially closed, so long as a valve is provided. In a valve bag, the purchaser end is closed in the second manner described above. The tubular bag form is flattened somewhat, and the in-folded flaps correspond to the two opposite "short" sides of the bag. The in-folded flaps may or may not overlap. The outer flaps, which correspond to the "long" sides of the bag, are then folded over one another, and glued to each other. In addition, one of the in-folded flaps may be glued to one or more of the outer flaps. The remaining in-folded flap is typically not glued to either the outer flaps or the other in-folded flap, and so a channel is often formed, upon outward deflection of the glued and overlapped outer flaps, leading to the interior of the bag. If the in-folded flaps overlap, the flap is located on the side of the "under" flap. Filling can be accomplished by the insertion of an appropriately configured nozzle, which will extend to the gap between the in-folded flaps, to drop material into the interior of the bag, or if the in-folded flaps overlap, the nozzle will project under the "over" flap and into the bag far enough to clear the "under" flap and access the interior of the bag. After filling, the valve may then be closed by some suitable manner, such as by folding over and gluing down the end of the flap to the side of the bag, or by sealing the end of the valve such as with ultrasonic or thermal sealing (such as when the interior of the valve is provided with a polyethylene film liner or coating or an adhesive coating of some form). However, although all of the flaps have been folded over and glued, in a typical prior art construction valve bag, such as that illustrated in FIG. 1 and FIG. 2, there remain several points of possible leakage, through, for example, powder migration, wherein the various folded over flaps have resulted in several potential channels for access to the interior of the bag. Although such channels may be labyrinthine in nature, there still remains the possibility of some migration, sifting or puffing out of the granular, powdery or particulate material from the interior of the bag when the bag is being handled. Although such puffing or sifting can be avoided through the provision of a separately sealed liner to the bag, such as a polyethylene film liner, such liners add to the cost and complexity of the bag as well as to the cost and complexity of the filling and closure procedures.
Accordingly, it would be desirable to be able to provide a valve bag which is not provided with a separate, separately closed and entirely sealed liner, but which is provided with enhanced resistance to sifting or puffing out of particulate material, after filling of the bag and during the subsequent handling of same.
This and other objects of the invention will become apparent in view of the present specification (including claims) and drawings.